This is how the extrusion works on 3D Printers

3D printers are now trendier than ever. We can now purchase a wide range of 3D printers of different prices and sizes, and which print different materials. Some you can even put together yourself, such as the Prusa i3 Hephestos from BQ.

To operate and maintain any 3D printer, it is advisable (and imperative for the mentioned above, due to its DIY characteristics) to know how each component works, especially the extruder.

The extruder of a 3D printer is the component that takes the filament from the coil, and then precisely delivers it to the base surface according to the implemented settings, which the printer reads from the GCODE file to generate each layer of the print.

Do you know how extruders work and the various types that exist? These are always very important things to know. If your printer jams or the filament breaks inside the extruder, it may be necessary to take the printer apart and solve the problem yourself. But worry not, we will show you how everything works.

The extruder is a device composed of various parts with characteristics that vary from one printer to the next. The extruder and electronics can be changed and adapted depending on the printer, but that would be a subject for another article.

The extruder is composed of:

  • Stepper motor: This motor is used to push the filament from the coil all the way to nozzle in order to deliver each layer of the ongoing print. The motor is controlled by the electronics of the printer, and rotates using very short steps in order to deliver the exact amount of material needed.
  • Drive gear: The drive gear is the part attached to the axis of the stepper motor, like a staggered or grooved rim pulley. Its function is to apply traction to push the filament as the stepper motor turns.
  • Reduction gear (Wade System): In some cases, a gear bigger than the one locked on the motor axis is used to increase the force applied to the filament. In our case, that’s the gear that makes direct contact with the filament itself. The motor forwards the turn so that the reduction does as well.
  • Hot-end: The hot-end is the component in charge of heating and melting the filament so that it liquefies enough to go through the nozzle of the extruder. It is a vertical tube which the filament passes through while still solid. The filament heats up from the outside while it passes so that the temperature reaches the interior, affecting the filament in the correct way.
  • Thermistor: The thermistor is the element in charge of measuring the temperature and forwarding the information obtained to the printer’s control system, making sure that the temperature of the extruder is managed correctly, as this will be the temperature that the filament will be at when leaving the nozzle.
  • Nozzle: The nozzle is a simple cone with a wide side through which the hot material enters and accumulates, maintaining its heat before exiting, melted, through a very narrow opening. The diameter of this opening in the Witbox and the Prusa i3 Hephestos is 0.4 mm.

Up until here we could say that all extruders are the same. All extruders have the same elements, although the dimensions may vary depending on the extruder (there are filaments of 1.75 and 3 mm in diameter and coils of 0.4 and 0.8 mm, among others). There are two forms of extrusion: direct extrusion and Bowden extrusion. Here is a detailed description of each one:

Direct Extrusion

The direct extrusion system is the most simple and effective, and is recommended for beginners. This is the system used by the Prusa i3 Hephestos and the Witbox 3D.

This extrusion method pulls the filament from the motor, through the hot-end, and directly to the nozzle. The extruder comes as a single part, which is detachable and more compact.

Some of the advantages of this type of extrusion are:

  • Compact extruder
  • Easy checking of damage or jam resolution
  • Completely detachable

But, as with everything, it also has some disadvantages:

  • The whole set is heavier, which affects the Y and X axes.

Below are some pictures of the extruders of BQ 3D printers, showing every component.

Prusa i3 Hephestos extruder

Prusa i3 Hephestos extruder

Another view of the Hephestos extruder

Another view of the Hephestos extruder

In the following image, you can observe how the filament goes straight from the entrance of the extruder to the hot-end, and how it is pulled through by the drive gear.

View of the direct extrusion system

View of the direct extrusion system

Bowden Extrusion

The components and the way the filament reaches the nozzle from the coil are very similar to the ones in the previous method. Here however, the motor is separated from the hot-end and the filament is taken to the X axis carriage through a flexible pipeline.

Some advantages are:

  • It’s separated from the hot-end, so the motor is the only thing on the “X” axis, consequently adding less weight to it.
  • The “X” axis moves better because it carries less weight.
  • As it is only used on the carriage, the hot-end can be reduced in size.

As disadvantages we could mention:

  • Its system is more complex to build and maintain
  • It’s more sensitive to errors
  • It is more likely to overflow

An example of a Bowden extruder is shown below:

Bowden extruder

Bowden extruder

In any case, both extruders fulfil their purpose. They both extrude and correctly place the material in order to build the object. Basically, they are two ways of achieving the same result, so it is more a matter of personal taste.